This invention relates to a magnetic disk drive and more particularly to a magnetic disk drive in which a magnetic circuit for driving a carriage is supported and which is capable of improving the accuracy with which a magnetic head for recording and reading information is moved and positioned at a predetermined point of a magnetic disk as magnetic recording medium.
A magnetic disk drive, as soon as it is required to write and read on a magnetic disk, has to rapidly move a magnetic head in the radial direction of the magnetic disk so as to position it over the specified track. Therefore, for high-density recording and high-speed data processing, it is effective to reduce errors in positioning of the magnetic head and to store the data at narrower track pitch.
As for a magnetic circuit used as a driving means for positioning the magnetic head over the desired track of the magnetic disk, a voice coil motor (referred to as xe2x80x9cVCMxe2x80x9d, hereinafter) is generally used which comprises a driving coil, permanent magnet, and yoke. The driving coil is fixed to a carriage, and the magnet and yoke (referred to as xe2x80x9cmagnet-yoke assemblyxe2x80x9d, hereinafter) are fixed on a housing. It has been general to support the magnet-yoke assembly by fixing it directly to the housing with a plurality of screws.
However, when the driving coil fixed to the carriage is applied with electric current to generate a driving force, the resultant reaction is exerted on the magnet-yoke assembly to cause the housing to vibrate through the screws. Due to this vibrating force, the means for rotating the magnetic disk is vibrated and hence the magnetic disk is vibrated. As a consequence, relative displacement takes place between the magnetic head supported by the carriage and the magnetic disk at the time of positioning, and therefore it is necessary to reduce the structural vibration attributed to the driving reaction of the VCM in order to achieve high-speed and high-precision positioning.
As means for solving the above problems, there is known a technology disclosed in JP-A-1-137476, for example. In this example, the magnet-yoke assembly is fixed to the housing through an antivibration member at its lower surface, and therefore the vibration of the VCM caused by the movement of the carriage is restrained from being transmitted to the housing.
Further, as means for reducing the vibration of the rotating means on which the magnetic disk is set, there is known a technology disclosed in JP-A-64-39685, for example. In this example, the magnet-yoke assembly is supported in the housing through a damper at its upper and lower surfaces and an elastic member at its side surfaces, and therefore it is possible to reduce the transmission of reaction to the magnetic disk even if the frequency of the vibration of the VCM caused by the driving reaction agrees with that of the damped vibration of the rotating means.
However, in the conventional technology disclosed in JP-A-1-137476, the vibration of the magnet-yoke assembly caused due to the driving reaction of the carriage can be damped, but the direction of motion of the magnet-yoke assembly is not controlled. When the apparatus is applied with external force such as vibration, impact and so on, the magnet-yoke assembly is vibrated not only in the oscillating direction but also in the axial direction of the carriage to cause relative displacement to take place between the permanent magnet and the driving coil in the direction of gap, with the result that it is difficult to keep the gap between them constant.
Therefore, there is a danger that the permanent magnet and the driving coil are brought into contact with each other, giving rise to a problem that the size, particularly the thickness of the permanent magnet cannot be made large enough to obtain the carriage driving force sufficiently. To solve this problem, it is necessary to increase the thickness of the apparatus, which makes it difficult to be thinner.
On the other hand, in the conventional technology disclosed in JP-A-64-39685, the magnet-yoke assembly is supported and fixed in the hung state through the damper of rubber member and the elastic member of leaf spring, thus providing an antivibration structure. The rubber member and the leaf spring are of the shapes that allow for reduction in peak of the resonance of a spindle support system on which the magnetic disk is set. When the magnet-yoke assembly is supported through the rubber member, since the rubber member changes greatly in its own rigidity and damping characteristics with temperature, the antivibration structure of the support system can show only a small effect according to the kind and arrangement conditions of rubber member and the environmental conditions of the apparatus, giving rise to a problem that the effect of making the reduction in resonance of the spindle support system reach the target is not always shown satisfactorily.
An object of the present invention is to provide a magnetic disk drive which overcomes the above problems of the prior arts and in which a magnetic circuit is supported effectively in order to improve the accuracy of positioning a magnetic head.
It is possible to efficiently damp the vibration of a magnet-yoke assembly, provided that the driving reaction allows the magnet-yoke assembly to move only in the oscillating direction of a driving coil. In order to solve the above problems, the present invention mainly adopts the following constructions.
There is provided a magnetic disk drive comprising a plurality of magnetic disks as magnetic recording medium, a rotating means for rotating the magnetic disk, a carriage holding a magnetic head for recording and reading information on the magnetic disk, a magnetic circuit for giving a driving force to the carriage so as to position the magnetic head at an arbitrary point in the radial direction of the magnetic disk, and a housing including a base and a cover, wherein the magnetic circuit comprises a driving coil attached fixedly to the carriage and a magnet-yoke assembly in which magnet and yoke are integrated, and the magnet-yoke assembly is supported in the housing at one point thereof so as to be able to rotate in the direction parallel to the surface of the magnetic disk.
Preferably, the magnet-yoke assembly is rotatably supported by means of a bearing, and the bearing is given with an initial displacement to increase the axial bearing rigidity thereof.
Further, it is preferred that the base or the cover is provided with a slip guide so as to rotate the magnet-yoke assembly on the slip guide surface with low friction and give an initial displacement to the bearing.